This invention relates to an exhaust gas processing device for a fuel cell used as a power source of an electric vehicle.
A fuel cell system is provided as a power source in an electric vehicle (hereinafter referred to simply as “vehicle”), and in cases, for example, where pure hydrogen (hereinafter referred to simply as “hydrogen”) is used for fuelling the fuel cell system, a hydrogen supply ductwork for the fuel cell system includes a recirculation system which is connected to an anode vent of a fuel cell stack and adapted to recirculate anode exhaust gas in order to improve utilization efficiency of hydrogen and thus to enhance fuel economy of the electric vehicle (e.g., see Japanese Laid-Open Patent Application, Publication No. 6-275300).
To circulate (and recirculate) hydrogen, a variety of devices are available, which include: a blower that produces a current of hydrogen, an ejector that produces a suction pressure to withdraw hydrogen, a vacuum pump, and the like. In the recirculation system, as recirculation continues for a long time, the concentration of impurities, such as nitrogen, in hydrogen would increase in most instances, which would cause the efficiency of electric power generation to decrease. The anode exhaust gas which contains impurities but still has a high concentration of hydrogen should not be released as it stands.
Accordingly, the fuel cell system is provided with a diluter in which the anode exhaust gas containing unreacted hydrogen is diluted so as to have a lower concentration of hydrogen before it is discharged to the outside of the fuel cell system. Moisture or water discharged together with hydrogen from the fuel cells could build up in pipes of the recirculation system connected to the anode vent of the fuel cell stack, and would disadvantageously impede the normal flow of hydrogen in the pipes of the recirculation system. Such moisture or water may also be discharged via the diluter to the outside of the fuel cell system.
Thus, the unreacted hydrogen is purged from the anode of the fuel cell stack and diluted with exhaust gas in the diluter, though such arrangement is not disclosed in the aforementioned reference.
Accordingly, the fuel cell system is adapted to force the hydrogen containing impurities such as nitrogen to be purged and discharged together with the moisture or water to the outside at frequent times, e.g., when the vehicle stops to wait at traffic lights. However, when a starter switch is turned off to stop a motor of the vehicle, the generation of electric power in the fuel cell stack stops entirely, and thus the flow of the cathode exhaust gas (cathode off gas as exhaust air) stops at the same time. Therefore, hydrogen that has not been discharged remains in the diluter. The hydrogen remaining in the diluter, if left untreated, diffuses spontaneously, and would disadvantageously flow back to the fuel cell stack and pipes.
The present invention has been made to address the above-described disadvantages. Therefore, it is an exemplary general object of the present invention to provide a device that can reduce a concentration of hydrogen remaining in the diluter and discharge the same to the outside, even after the generation of electric power in the fuel cell stops.